Turbine engines are used in many fields, principally as drives in the aviation industry and for energy production. In energy production, a distinction is made between gas turbines and steam turbines, which are both used, often simultaneously in so-called gas and steam installations, for driving generators. In the gas turbine, which is examined below, a fuel/air mixture is ignited in a combustion chamber, from where the working medium produced in this process expands in the direction of the blades, performing work as it passes said blades. The energy of the working medium is converted by means of the blades into kinetic energy, which, upon rotation of the turbine shaft, is relayed to generators.
The fuel/air mixture usually burns at a temperature of 1200° C. to 1300° C., producing low emissions and thereby achieving a high degree of efficiency. The degree of efficiency can generally be further increased through a further rise in the combustion temperature.
At these high combustion temperatures of the working medium, very high demands in terms of thermal endurance, mechanical strength and service life are placed on those components of the turbine engine which come into contact with the working medium. A maximum possible degree of efficiency should be achieved here, taking into account the risk to operations and cost-effectiveness of the individual components.
Thermal endurance, a long service life and reliability are also required of the blades of a turbine engine. In order for the blades in the first row of blades, viewed in the direction of flow of the working medium, to withstand the highest thermal loadings, they are cooled in a known manner. For this purpose, they generally have cavities running through them, said cavities forming a branched system of channels in which a coolant flows. Either compressed air or steam, or else both simultaneously, is/are used as a coolant. Steam exhibits better cooling properties than compressed air. However, steam places higher demands on the sealing of the complete cooling system, which means higher production costs with regard to conduction of the coolant.
It is known that blades can be air-cooled and/or steam-cooled. Air cooling can take the form of open as well as closed cooling, but steam cooling is appropriate only as a closed cooling system. When blades of a turbine engine are cooled, the substantial difference in pressure between working medium and coolant can be maintained only by means of a high level of technical resources. In order to close off areas from one another, a costly sealing system is required along the conduction pathway of the coolant, so as to limit leakage losses and thereby ensure efficient cooling. Disadvantageous here is the enormous economic and technological outlay required for this purpose, which on top of everything leads to a reduction in operational dependability and reliability on account of the complicated technology.
Supplying coolant to individual blades in the various rows of blades is very difficult, due to the arrangement of the individual elements concerned, and demands a high outlay in order to guarantee the required sealing of the system and a low operating risk.